HP B9180 Squeaks when printing

My B9180 emits a loud squeak, similar to an unlubricated door hinge sound, when it is printing. To anyone with mechanical sympathy it is not a good sound! I do not think it is the head moving back and forward along the stainless bar as that looks good and has a smear of light grease. I did try one drop of light oil on the stainless bar to no avail. Printing quality does not appear to be affected at this stage. Any ideas would be much appreciated. HP want me to purchase another printer at a discounted rate and return mine to them as mine is out of warranty.
Apart from this problem the printer has been great with excellent results.